As shown in FIG. 13, conventional light emitting element drive device 1d is known including light emitting element 2, drive unit 3 for driving light emitting element 2, electricity storage element 4 capable of storing electric power, battery power supply 6 capable of supplying electric power to electricity storage element 4, and boost chopper circuit 9 having inductor 91, for boosting voltage by opening and closing switching element 92. Boost chopper circuit 9 includes diode 93.
Light emitting element drive device 1d further includes camera unit 7 capable of imaging, control unit 8 for controlling the entire device, and limiting resistor 44 for limiting a current flowing through light emitting element 2. Control unit 8 includes drive control unit 81 for controlling drive unit 3 and chopper control unit 82 for controlling boost chopper circuit 9.
Drive unit 3, with first and second switch units (CMOS) 12 and 13 provided, is switchable between two states: a state (hereinafter also referred to as a storing state) in which electric power from battery power supply 6 is boosted by boost chopper circuit 9 and is stored in electricity storage element 4; and a state (hereinafter also referred to as a discharging state) in which the electric power stored in electricity storage element 4 is supplied to light emitting element 2 (refer to patent literature 1 for example). The following describes the storing state and the discharging state.
In the storing state, drive control unit 81 outputs an H signal to first CMOS 12 to cause the H signal to be applied to the input of the gate of first CMOS 12, which is thus turned on (close). Meanwhile, drive control unit 81 outputs an L signal to second CMOS 13 to cause the L signal to be applied to the input of the gate of second CMOS 13, which is thus turned off (open).
Consequently, current i1 flows from battery power supply 6 through the closed loop of first CMOS 12, inductor 91, diode 93, and electricity storage element 4, causing electricity storage element 4 to store electric power supplied from battery power supply 6. At this moment, chopper control unit 82 opens and closes switching element 92 rapidly and periodically, which boosts electric power (voltage) from battery power supply 6 and stores electric power in electricity storage element 4.
In the discharging state, drive control unit 81 outputs an L signal to first CMOS 12 to cause the L signal to be applied to the input of the gate of first CMOS 12, which is thus turned off (open). Meanwhile, drive control unit 81 outputs an H signal to second CMOS 13 to cause the H signal to be applied to the input of the gate of second CMOS 13, which is thus turned on (close).
Consequently, current i2 flows through the closed loop of electricity storage element 4, limiting resistor 44, light emitting element 2, and second CMOS 13, causing electricity storage element 4 to supply electric power to light emitting element 2, which thus light emitting element 2 emits light.
In the meantime, in order that light emitting element drive device 1d shown in FIG. 13 causes light emitting element 2 to emit light again, electricity storage element 4 that has discharged needs to store electric power again. Thus, in a case where short-interval (continuous) light emission (i.e. imaging) is required, electricity storage element 4 fails to store electric power within an appropriate time, which disables imaging at desired timing.
Further, as shown in FIG. 14, light emitting element drive device 1e is known including light emitting element 2; drive unit 3 for driving light emitting element 2; first and second electricity storage elements 4 and 5 capable of storing electric power; and battery power supply 6 capable of supplying electric power to drive unit 3 and each electricity storage elements 4 and 5. Light emitting element drive device 1e further includes camera unit 7 capable of imaging; control unit 8 for controlling the entire device; boost unit 9 for boosting electric power supplied from battery power supply 6; and balancing resistors 10 for evenly storing electric power in series-connected each electricity storage elements 4 and 5.
In light emitting element drive device 1e, with inverter (NOT gate) 11 and first and second switch units (CMOS) 12 and 13 provided, drive unit 3 is switchable between two states: a storing state in which each electricity storage elements 4 and 5 store electric power from battery power supply 6; and a discharging state in which the electric power stored in each electricity storage elements 4 and 5 is supplied to light emitting element 2 (refer to patent literature 1 for example). The following describes the storing state and discharging state.
In the storing state, when drive control unit 8 outputs an L signal, the L signal is applied to the input of inverter 11, and thus an H signal is applied to the input of the gate of first CMOS 12, which is thus turned on (close). Meanwhile, the L signal is applied to the input of the gate of second CMOS 13, which is thus turned off (open). Consequently, current i1 flows from battery power supply 6 through the closed loop of first CMOS 12, boost unit 9, and each electricity storage elements 4 and 5, which causes each electricity storage elements 4 and 5 to store electric power supplied from battery power supply 6.
In the discharging state, when drive control unit 8 outputs an H signal to activate the circuit, the H signal is applied to the input of inverter 11, and thus an L signal is applied to the input of the gate of first CMOS 12, which is thus turned off (open). Meanwhile, the H signal is applied to the input of the gate of second CMOS 13, which is thus turned on (close). Consequently, current i2 flows through the closed loop of electricity storage elements 4 and 5, light emitting element 2, and second CMOS 13 to cause each electricity storage elements 4 and 5 to supply electric power to light emitting element 2, which thus light emitting element 2 emits light.
In the meantime, with light emitting element drive device 1e shown in FIG. 14, battery power supply 6 can supply electric power with a voltage of 3.6 V; each electricity storage elements 4 and 5, 2.5 V, for example; however, light emitting element 2 requires 4.0 V for emitting light, which is higher than those voltages. Hence, boost unit 9 is provided and two electricity storage elements 4 and 5 are serially connected.
Concretely, in the storing state, boost unit 9 boosts a voltage of 3.6 V supplied from battery power supply 6 to 5.0 V to allow two electricity storage elements 4 and 5 to store electric power to an added voltage value of 5.0 V. In the discharging state, two electricity storage elements 4 and 5 discharge electric power with an added voltage value of 5.0 V, which allows supplying electric power with a voltage higher than that supplied from battery power supply 6 or a single electricity storage element 4 (or 5) to light emitting element 2, which thus light emitting element 2 emits light.
However, to cause light emitting element 2 to emit light again, two electricity storage elements 4 and 5 that have discharged need to store electric power again. Thus, in a case where short-interval (continuous) light emission (i.e. imaging) is required, each electricity storage elements 4 and 5 fail to store electric power within an appropriate time, which disables imaging at desired timing.